The invention relates to an iron oxide-silicon dioxide-titanium dioxide mixed oxide, the process for producing it and its use.
The production of titanium dioxide by pyrogenic means, primarily by flame hydrolysis, is known (DE-PS 830 786). A titanium dioxide produced in this way can be used in sunscreens as a UV absorber which is, at the same time, transparent to visible light. It can also be used in lacquers or plastics.
The production of mixed oxides by pyrogenic means is known from the documents DE-A 952 891, DE-A 29 31 585, DE-A 24 31 810 and DE-A 36 11 449.
JP-A-5330825 discloses titanium dioxide doped with iron oxide, which is produced by precipitation and is preferably coated with further oxides.
Flame-hydrolysis can be used also to produce titanium dioxide powder containing iron oxide, as disclosed in EP 0 609 533 B1. Particular applications, such as for example as a UV absorber in sunscreens, require particularly high absorbency of UV radiation, in particular UVB radiation, and transparency, which cannot be achieved with the known titanium dioxide.
The invention provides an iron oxide-silicon dioxide-titanium dioxide mixed oxide produced pyrogenically, in particular by flame hydrolysis. It can consist of a pyrogenically, in particular flame-hydrolytically-produced ternary iron oxide-silicon dioxide-titanium dioxide mixed oxide with a specific surface of 10-200 m2/g, which contains 0.5 to 50 wt. % iron oxide and 0.5-50 wt. % silicon dioxide, in relation to the total quantity, as constituents of the ternary mixed oxide.
The invention further provides a process for the production of the iron oxide-silicon dioxide-titanium dioxide mixed oxide, which is characterised in that vapourable iron compounds are vapourised and transferred to the mixing chamber of a known burner, vapourable silicon compounds and titanium compounds are at the same time dosed separately and vapourised together and also transferred to the mixing chamber of the known burner, the vapourised gaseous compounds being dosed in a ratio equivalent to the composition of the iron oxide-silicon dioxide-titanium dioxide mixed oxide, the gaseous compounds are mixed in the mixing chamber of the known burner with (core) hydrogen and (core) oxygen and/or (core) air and the gas mixture which flows out of the nozzle opening of the burner is burned in the reaction chamber of the burner, (shell) hydrogen and optionally (shell) nitrogen also being fed into the ring nozzle surrounding the burner throat, the iron oxide-silicon dioxide-titanium dioxide mixed oxide formed is separated from the gaseous reaction products and optionally liberated from adhering reaction products by means of water vapour.
The iron oxide-silicon dioxide-titanium dioxide mixed oxide can be produced by vapourising anhydrous iron (III) chloride, transferring it together with an inert gas, for example nitrogen, to the mixing chamber of a known burner, mixing it there with hydrogen, air and a mixture of gaseous titanium tetrachloride and silicon tetrachloride, which is dosed separately but vapourised together, optionally with a carrier gas, which can be inert, such as for example nitrogen and/or air, in a ratio equivalent to the composition of the iron oxide-silicon dioxide-titanium dioxide mixed oxide, burning the multi-component mixture in the reaction chamber (flame tube) of the burner, (shell) hydrogen and optionally (shell) nitrogen also being fed into the ring nozzle surrounding the burner throat, then separating the solid from the gaseous reaction products and optionally liberating them from adhering reaction products in moist air.
A burner device as disclosed in the document EP 0 814 057 B1 can be used for the process according to the invention.
In a preferred embodiment the iron oxide-silicon dioxide-titanium dioxide mixed oxide may have the following physical-chemical data:
The iron oxide-silicon dioxide-titanium dioxide mixed oxide obtained has very fine particles and is very homogenous and very pure. It has better absorption of and thus poorer transparency to UV light combined with extensive transparency to visible light, than the prior art. It disperses easily in a particular medium, for example a sunscreen.
The iron oxide-silicon dioxide-titanium dioxide mixed oxide can also be used for the production of cosmetics, lacquers, catalysts, catalyst carriers and photocatalysts and as a UV absorber.
The invention also provides skin cosmetics which contain the iron oxide-silicon dioxide-titanium dioxide mixed oxide according to the invention, preferably in a quantity of 0.05-10 wt. %.